Having problems making transparent plastic in Blender cycles
My method is more based on feeling rather than a rational explanation of physically based values.
Examining various plastic references as your example, it appears much brighter than glas. There also seems to be some diffuse/translucent scattering which you tried to add with the transluceny BSDF.
This is the final node setup.

Here are various example of shaders.


To the right is a plain glass shader. It seems to have more Glossy Reflections and more clear refractions than plastic should have. There are also very dark areas which appear because of the refraction. Plastic has close to no black.
To the left is a shader which resembles plastic more.It mainly consists of a mixed Glossy and Refractions BSDF. If you look at IOR values, plastic ranges around 1.49 (used in the refraction shader).It still doesn't have the add shader depicted in the node setup. That's why it appears to be more see through and more glassy.
Then we add the Add Shader after the Refraction, and mix it with a Transparent BSDF. When combining Transparent BSDFs with the add shader, more light is added. This is obviously not physically correct, but sort of creates a plastic feeling which is probably caused by imperfections in the surface in reality.
Finally, I mixed in a Diffuse BSDF at the end. The factor is a very small noise value. You did something similiar with using the translucency BSDF. I'd advise you against that, because you don't have the proper IOR. If you want the Refraction to be more unclear or blurred you can always use the Roughness value. The outcome is used by the center objects in the image.


Examination

Although the render is bad, the brightness from the added Transparency BSDF makes the material resemble plastic.

BUT, don't forget

You will only achieve the proper result with the fitting lighting.
The material only does a small part. The main work is done by modelling the base and the imperfections in the right scale and proportion. The small details can also come from bump maps. Try using a solidy modifier on your model!
Imperfections: uneven thickness, seams, ridges, dents/bends, roughness on the inside. It is more difficult to make a convincing geometrically perfect model rather than a naturally distorted one.



Modeling

The shader doesn't quite look right, yet. Maybe there should be more of the diffuse component of some slight roughness in the refraction. There is also no thickness to it, in this case the solidify modifier is required.
Nevertheless, the viewer will probably be convinced that this is plastic, becuase of the shape and imperfections. Even if we used a glass shader it would be interpreted as plastic, because only glass would usually not be found in the surface shapes.




Same principle with a normal map. The Transparency shader not that bright in this case, because I had to place an emission shader underneath. Therefore I simply increased the roughness on the Refraction to increase the scattering towards the camera. Already this drawback makes it look more like glass. The sharp edges on the material can also be interpreted as glass compare to the smooth rounded shapes of plastic.